In communications technologies, a base station allocates, to each user equipment (UE) in advance, some dedicated resources for transmitting channel state information (CSI), so as to help the base station arrange downlink transmission.
With continuous evolution of a Long Term Evolution (LTE) technology, a quantity of cells that can be used by the UE is expanded in the 3rd Generation Partnership Project (3GPP), and an amount of CSI that needs to be reported by the UE increases accordingly.
Currently, the UE reports CSI in two manners: periodic CSI reporting and aperiodic CSI reporting.
In the periodic CSI reporting, a reporting interval is generally long, and consequently, the base station cannot learn of a channel status of the UE in a timely manner, resulting in low spectrum efficiency. In addition, a large quantity of physical uplink control channel (PUCCH) resources are consumed in this manner.
In the aperiodic CSI reporting, the base station needs to continuously allocate dynamic physical uplink shared channel (PUSCH) resources to the UE, and instructs the UE to transmit CSI together with data. Even if there is no uplink data to be transmitted, the UE still needs to perform this operation. Consequently, a large quantity of PUSCH resources are consumed in this manner. If the UE needs to transmit a large amount of downlink data but little uplink data, a large quantity of physical downlink control channel (PDCCH) resources and PUSCH resources need to be consumed to transmit CSI.
Therefore, when the UE uses a large quantity of cells, how the base station can reliably obtain, in a timely manner with low costs, CSI that is of a cell and that is reported by the UE, and can efficiently arrange sending of downlink data is a problem that currently needs to be resolved.